The interaction of chemical carcinogens with the genome of a target cell is being studied by: 1) examining the binding of benzo(a)pyrene to SV40 minichromosomes, 2) examining the binding of benzo(a)pyrene to polytene chromosomes, and 3) developing monoclonal antibodies to DNA which has been modified by diol epoxide I. An antibody detection technique which allows detection of one carcinogen adduct per molecule of DNA has been developed. Homogenates of Chironomus thummi metabolize benzo(a)pyrene. Diol epoxide I binds to polytene chromosomes in a random fashion. The carcinogen does not bind to a selected genetic locus. Mice immunized with diol epoxide I-modified DNA produce antibodies which will react with the immunogen, but not with unmodified DNA.